1. Field of the Invention
The invention relates to a vortex flow meter comprising a measurement tube through which a medium can flow, an obstacle provided in the measurement tube for generating vortices in the medium and a deflection body which is provided in the region of action of the obstacle and can be deflected by the pressure variations associated with the vortices in the medium.
2. Description of Related Art
Vortex flow meters have been known for a long time, the measurement principle being based on the fact that a vortex street can form in a liquid or gaseous medium behind an obstacle around which the medium flows, this vortex street being formed by vortices shed from the obstacle and progressing with the flow. The frequency with which vortices are shed from the obstacle depends on the flow rate; with certain assumptions, this relationship is almost linear. In any event, measurement of the vortex frequency constitutes a suitable means for determining the flow rate of the medium, for which reason determination of the volume and mass throughput is possible indirectly—additionally taking into account, e.g., pressure and temperature—through the vortex frequency measurement. The vortices of the medium, which occur in a vortex street, lead to local pressure variations which act on the deflection body and are detected by it. The deflection body may be a pressure transducer, which is produced for example, using piezo elements or capacitive pressure sensors in which, albeit to a small extent, a sensor element experiences a deflection.
What is important is merely that the deflection body is arranged in the vortex street so that the vortices generated by the obstacle pass—at least indirectly—past the deflection body and are therefore detectable. To this end, the deflection body may be provided downstream behind the obstacle, in which case the obstacle and the deflection body are in fact produced physically separately. The deflection body may, however, also be the obstacle itself or be formed in the obstacle, for example, when, in the solution known from the prior art with pressure transducers, the pressure transducers are arranged over or in the obstacle and the pressure variations in the vortex street are thereby registered indirectly via channels; in this case, at least, the obstacle and the deflection body are produced physically in one unit.
In the methods known from the prior art for registering the movement of the deflection body, in which capacitive or inductive effects are used and in which operation is carried out with piezoceramics or in which optical fibers are also used to register the deflection, the deflection bodies must, respectively, be contacted by electrical or optical lines, these lines needing to be fed out of the medium-filled space through the measurement tube wall, or the housing of the vortex flow meter, into a medium-free space, usually to evaluation electronics. These feed-throughs have to be produced with very elaborate seals since—depending on the application—high pressure and/or temperature stability has to be achieved (several hundreds of bars or several hundreds of ° C.).